In an optical reproductive scanning apparatus used in a copier or a printer, a laser beam, including image information emitted from a laser source and appropriately modulated, enters a deflection system such as a polygon mirror, and then the deflected laser beam is projected onto an image carrier such as a sensitized drum to form an electrostatic latent image thereon. The electrostatic latent image is developed using toner to create a toner image which, in turn, is transferred to a transfer medium such as a recording chart to form an image. Well-known color image forming devices such as color copiers and color printers include a tandem-type image forming device in which plural image carriers such as sensitized drums are juxtaposed. Laser beams including yellow (Y), magenta (M), cyan (C), and black (BK) image data are separately scanned over the image carriers to create latent images. Then, the latent images are developed using toners. Toner images are transferred to a transfer medium such as a recording material moving along the juxtaposed image carriers to create a color image. The direction in which an electrostatic latent image is formed using a deflection device, such as a polygon mirror, is termed the main scanning direction and the direction in which an electrostatic latent image is formed by rotating a sensitized drum or an image carrier is termed the sub-scanning direction.
In order to ensure clearly formed images using multiple scanning beams, the scanning beams need to maintain precise optical properties, which is based on the scanning apparatus maintaining its scanning properties. To ensure the desired optical and scanning properties, an optical reproductive scanning apparatus should include optical elements mounted with high precision and mounted for high precision movement. A slight shift in the reflecting direction of the reflecting mirror or changes in the mounting condition of the reflecting mirror may impair the optical and scanning properties. Therefore, the reflecting direction of the reflecting mirror should be adjusted with high precision. When the reflecting mirror that reflects scanning light reflected by a polygon mirror has an elongated shape, such as a strap, is supported at both ends and is movable over a scanning range, changes in mounting conditions at one of the ends may cause the entire reflecting surface to undergo an undesired movement, causing an undesired change in the reflected light. Therefore, both ends should be mounted and adjusted with high precision.
Conventional adjusting mechanisms for such reflecting mirrors include, for example, a mirror adjusting mechanism as described in the Japanese Laid-Open Patent Application No. H5-33108. This mirror adjusting mechanism comprises bearing members at the ends of a mirror frame that can abut against the reflecting surface of a mirror. The bearing member is provided with an adjuster plate that is rotatably mounted thereon and can abut against the reflecting surface of a mirror. The adjuster plate is provided with an adjusting member to adjust its rotation. In addition, an urging member is provided that abuts against the back of the mirror frame so as to press on the mirror. The adjusting member is adjusted to rotate the adjuster plate, which causes the mirror to swing about a longitudinal axis of the mirror, changing the orientation of the reflecting surface.
Japanese Laid-Open Utility Model Application No. H6-148490 describes an optical member holding mechanism of a beam scanning optical system. This optical member holding mechanism has a structure in which holes and a small projection are formed in the side boards of a housing for an optical device. Both ends of a flat mirror are loosely fitted in the holes. Press plates are fixed to side boards of the mechanism from the outside so that they are free to rotate about points that are different from points defined by fixing screws. Press pieces provided on the press plates abut against the back of the mirror. The press plates are fixed to the side boards by the fixing screws and the press plates are rotated to adjust the inclination of the mirror by a combination of an elongated hole formed in the press plate and an eccentric pin that is rotated.
In optical reproductive scanning devices, the final mirror that reflects light to the image carrier of an optical reproductive scanning device is, in some cases, an elongated cylindrical mirror. A cylindrical mirror is used in order to provide a magnified image of a desired magnification to the image carrier. The cylindrical mirror may undergo changes in the magnification at the surface of the image carrier when it shifts in the normal direction, that is, in a direction that changes the optical path length between the cylindrical mirror and the image carrier. Additionally, the entrance point to the image carrier may change when the cylindrical mirror rotates about an axis parallel to the center of curvature of the cylindrical mirror. Further, the main scanning line may shift during rotation of the cylindrical mirror due to misalignment of the end pivots of the cylindrical mirror. Therefore, the cylindrical mirror requires adjustments for the position in the normal direction (hereinafter termed xe2x80x9cmagnification adjustmentxe2x80x9d), the entrance point by the rotation angle (hereinafter termed xe2x80x9cregistering adjustmentxe2x80x9d), and the relative positions of the both ends (hereinafter termed xe2x80x9cskew adjustmentxe2x80x9d). This mounting mechanism for a cylindrical mirror also uses a conventional mirror adjustment mechanism and an optical member holding mechanism.
The mirror adjustment mechanism described in the Japanese Laid-Open Utility Model Application No. H5-33108 rotates an adjuster plate that is in direct contact with the mirror. The adjuster plate is provided at one or both ends of the mirror. The mirror may be subject to distortion such as twisting or bending, depending on how the adjustment is performed. When the adjuster plate is provided at one end, the other end is restrained with a certain force. Therefore, when the adjuster plate is rotated to press and move the one end, the mirror may be bent or twisted. When adjuster plates are provided at both ends, adjustment should be performed on both ends, which makes the adjustment operation complicated and requires balanced adjustments in order to prevent mirror distortion.
An optical member retaining mechanism as described in the Japanese Laid-Open Patent Application No. H6-148490 uses press boards that are in contact with both ends of a mirror and serve as leaf springs to resiliently press the back of the mirror. Similarly to the mirror adjustment mechanism described in the preceding paragraph, the mirror may be distorted by bending or twisting due to the force of a press board pressing against one of the ends.
As described above, conventional mirror adjustment mechanisms and optical member retaining mechanisms require complicated mechanisms and processes for mounting and adjusting a cylindrical mirror. For example, when brackets are used, the brackets for mounting the mirror may slide to adjust the magnification, and adjuster plates or press boards may rotate to adjust registering and skew. Therefore, if the adjuster plates or press boards are rotated for the skew adjustment after the registering adjustment is completed, the position is lost and the registering adjustment must be repeated. Then, the registering and skew adjustments are repeated until a desired optical performance is obtained. This makes the adjustment operation difficult and time consuming, especially for inexperienced operators.
In view of the problems discussed above, the present applicant previously proposed a mounting and adjusting mechanism for a strap member that allows for mounting of a strap-shaped optical member, such as a mirror or lens, with the reflecting direction precisely adjusted and without distortion of the optical member, as set forth in Japanese Patent Application No. 2000-176901 (which corresponds to Japanese Laid Open Application No. 2001-356259). That mechanism allows for easy and reliable adjustment and movement of an optical member, such as a cylindrical mirror, in multiple directions.
As disclosed in that application, a cylindrical mirror is housed in a mirror holder that has at least one open side, with the reflecting surface of the cylindrical mirror being exposed through the open side. Bearing shafts are provided at both ends of the mirror holder, protruding from the mirror holder in the longitudinal direction of the cylindrical mirror. Retainer plates are loosely fitted on the respective bearing shafts, with the retainer plates being free to slide relative to the surfaces of frames on which the cylindrical mirror is mounted in a direction orthogonal to the bearing shafts. One of the retainer plates is a captive retainer plate that is loosely fitted on one of the bearing shafts with an appropriate clearance. The other retainer plate is loosely fitted on the other bearing shaft with an appropriate clearance so that it is free to be at a biased position. An engaging adjuster plate is detachably linked to the end of the bearing shaft that protrudes outward from the captive retainer plate. The engaging adjuster plate is rotatable relative to the captive retainer plate so as to rotate the mirror holder about the bearing shaft. An operational adjuster plate is linked to the end of the bearing shaft that protrudes outward from the other loosely fitted retainer plate. The operational adjuster plate is free to slide relative to the other loosely fitted retainer plate in a direction orthogonal to the normal of the cylindrical mirror, and both of the retainer plates are free to slide relative to the frames in the direction of the normal of the cylindrical mirror.
The retainer plates are slid relative to the frames for the magnification adjustment. The engaging adjuster plate is rotated relative to the captive retainer plate for the registering adjustment. The operational adjuster plate is slid relative to the loosely fitted retainer plate for the skew adjustment. These adjustments can be performed independently. Therefore, one adjustment is not necessarily done again after another, greatly facilitating the adjustment operation.
The operational retainer plate is loosely fitted on the bearing shaft to ensure a smooth rotation of the bearing shaft during registering adjustment. Without the smooth rotation, registering adjustment would be unreliable. However, this looseness may cause the bearing shaft to shift in relation to the operational adjuster plate due to vibrations and heating that occur during the operation of a copier or printer.
If this shift occurs after the skew and registering adjustments are done, imaging problems may occur, such as blurred colors in transferred images in a color copier. Therefore, the operational adjuster plate has a structure as shown in FIG. 16. As shown in FIG. 16, a clamp ring 50 having a cut part, or gap, where overlapping protrusions 51 are provided is prepared. The bearing shaft 52 is fitted within the clamp ring 50. A setscrew 53 is tightened through holes in the overlapping protrusions 51 so as to draw the protrusions closer together and thus hold the bearing shaft 52. After the registering adjustment, when the setscrew is tightened to fix the bearing shaft 52 in the clamp ring 50, the bearing shaft 52 may shift within the clamp ring 50. This may cause undesired changes in the skew adjustment that has already been performed. For this reason, the structure in FIG. 16 is not ideal.
The present invention relates to a mounting mechanism for a strap member in which the orientation of a surface of the strap member, such as a reflecting mirror, is adjustable. In particular, the strap member may be a cylindrical mirror for reflecting light beams to image carriers such as sensitized drums on which images are recorded in an optical reproductive scanning apparatus.
An object of the invention is to provide a mounting mechanism for a strap member in which the strap member can be readily fixed in position without causing positional changes of the strap member that would change the magnification and/or cause skew changes in scanning lines when the strap member is a cylindrical mirror in an optical scanning apparatus.